NPNs Flashcards
It is the major NPN in the blood; NPN present in the highest concentration in the blood.
Urea
Urea accounts for _____ % of NPNs
Urea accounts for 45% of NPNs in the blood.
Urea is the major excretory product of
Urea is the major excretory product of protein metabolism.
Urea is synthesized in the
It is synthesized in the liver from amino group and free ammonia generated during protein metabolism; it is synthesized in the liver from the deamination of amino acids
Urea is excreted by
Urea is excreted by the kidneys
Protein metabolism produces?
Protein metabolism produces amino acids which may be oxidized to
(1) produce energy
(2) stored as fat or glycogen
During protein metabolism, nitrogen is
During protein metabolism, nitrogen is released and produced as urea in the liver
Following its synthesis to the liver, urea is
Following its synthesis to the liver, urea is carried by the blood to the kidneys
In the kidneys, urea is
In the kidneys, urea is readily filtered by the glomerulus, where most urea is excreted in urine and some urea is reabsorbed substantially in the PCT (passive diffusion) and inner medullary collecting duct (active transport through urea transporters) during the passage of the filtrate in the renal tubules
Determinants of Urea Conc. in Plasma
Thus, the concentration of urea in the plasma is determined by:
1. renal function and perfusion
2. protein content in the diet
3. rate of protein metabolism
Purpose of Urea Measurement
Measurement of urea is used to:
(1) evaluate renal function
(2) assess the hydration status
(3) determine the nitrogen balance
(4) aid in the diagnosis of renal disease
(5) verify the adequacy of dialysis
Azotemia is the elevated concentration of
Azotemia is the elevated conc. of urea and nitrogenous compounds in the blood
Uremia is the very high or elevated
Uremia is the very high or elevated urea plasma concentration accompanied by renal failure. It is eventually fatal if not treated with dialysis and transplantation
Increased plasma urea is classified into
Increased plasma urea is classified into 3 main categories according to cause:
(1) Pre-renal azotemia
(2) Renal azotemia
(3) Post renal azotemia
Pre-renal azotemia is caused by
Pre-renal azotemia is caused by reduced blood flow; less blood is being delivered to the kidneys thus less urea is being filtered.
Pre-renal azotemia causes
congestive heart failure, hemorrhage, shock, dehydration, increased protein catabolism, corticosteroid therapy
Renal azotemia is caused by
Renal azotemia is caused by decreased renal function which causes an increase in plasma urea concentration due to compromised urea excretion by the kidneys
Renal azotemia causes
acute and chronic renal failure, glomerular nephritis, tubular necrosis
Post renal azotemia is caused by
Post renal azotemia is caused by obstruction of urine flow anywhere in the urinary tract (urinary tract obstruction)
Post renal azotemia causes
renal calculi, tumors in the prostate and bladder, severe infection
Decreased plasma urea concentration causes:
low protein intake, overhydration, severe liver disease, late pregnancy and infancy, severe vomiting and diarrhea, malnutrition
Specimens used for measurement of urea
plasma, serum, and urine
Anticoagulants Allowed for Urea Measurement
EDTA and Heparin (Sodium Heparin)
Anticoagulants NOT Allowed for Urea Measurement
Fluoride (Sodium Fluoride) and Citrate (Sodium Citrate) must be avoided
Why are fluoride and citrate avoided as anticoagulants in urea measurement?
Fluoride and citrate both inhibit urease
A fasting sample is (required/not required) for urea measurement.
Not required
Other specimen considerations for urea measurement
Nonhemolyzed samples are recommended; hemolyzed samples are avoided
Urine samples must be analyzed ASAP as urea is susceptible to bacterial decomposition; Urine samples which cannot be analyzed immediately must be refrigerated!
Timed (24-hour) samples must be refrigerated as well.
Urinary urea measurements may be used for
Urinary urea measurements may be used for the calculation of nitrogen balance
Reference Method For Urea Assay
Isotope Dilution Mass Spectrophotometry (IDMS)
What are the methods of urea analysis?
(1) Enzymatic Method of Urea Assay (Indirect Method)
- most frequently used in the clinical laboratory
- (a) Hydrolysis of Urea by Urease , (b) Coupled Urease/ Glutamate dehydrogenase (GLD) Method
(2) Chemical Method of Urea Assay
- (a) Diacetyl Monoxime Method
(3) IDMS
What are the methods of urea analysis?
(1) Enzymatic Method of Urea Assay (Indirect Method)
- most frequently used in the clinical laboratory
- (a) Hydrolysis of Urea by Urease , (b) Coupled Urease/ Glutamate dehydrogenase (GLD) Method
(2) Chemical Method of Urea Assay
- (a) Diacetyl Monoxime Method
(3) IDMS
Urease is aka
urea amidohydrolase, E.C. 3.5.1.5.
Urease hydrolyzes
Hydrolysis of Urea by Urease Principle: Urease hydrolyzes urea in the sample and the ammonium ion which is produced is quantified and may be treated with Berthelot reagents
Urease is produced from
Jackbeans
Creatinine is the end product of
Creatinine is the end product of muscle contraction and metabolism derived from creatine (alpha-methyl guanidoacetic acid) and phosphocreatine (a high energy-containing compound)
It is excreted in the plasma by the _____ at a rate related to ______
Creatinine is excreted in the plasma by the kidneys at a rate related to an individual’s muscle mass.
Creatinine measurements in serum and urine are done to
Creatinine measurements in serum and urine (creatinine clearance) are done to assess glomerular filtration rate (GFR)
Plasma creatinine is _____ to GFR
Plasma creatinine is inversely related to GFR
Creatinine is an index of
Creatinine is an index of overall renal function; it is commonly used to monitor renal function
Three Amino Acids that produce creatinine
Creatinine is produced by three (3) amino acids:
methionine, arginine, and lysine
Creatine is synthesized in the
Creatine is synthesized in the liver from AA - methionine, arginine, and lysine
Creatine is then transported to the
Creatine is then transported to the tissues (muscles) where it is converted to creatine phosphate or phosphocreatine - a high energy-containing compound
Creatine phosphate loses ____, whereas, creatine loses ______ and becomes
Creatine phosphate loses phosphoric acid, whereas creatine loses water and becomes creatinine- a cyclic compound
Creatinine diffuse into
Creatinine diffuses into the plasma and becomes excreted by the kidneys into urine
Creatinine is not
Creatinine is not reused by the body’s metabolism, it is not reabsorbed by the kidneys; thus it is solely a waste product
Creatinine is partially secreted by the
Creatinine is partially secreted by the proximal tubules via the organic cation pathway
Clinical Applications of Creatinine
Measurements of creatinine conc. are used to determine:
(1) determine the sufficiency of kidneys/renal function
(2) monitor the progression of kidney disease
(3) determine the severity of kidney disease/damage
(4) measure the completeness of a 24-hour urine collection
Plasma creatinine conc. is a function of:
(1) function of relative muscle mass- that is, the amount of creatinine generated is directly proportional to muscle mass
(2) function of turnover rate
(3) function of renal function (overall renal function)
